To a solution of 2-bromo-1-methoxy-4-methylbenzene (1.39 g, 15 mmol) in tetrahydrofuran (THF) was slowly added n-butyllithium (15 mmol) dropwise under nitrogen protection and -78 °C. The solution was stirred for 1 h. The solution was then mixed with tetramethyl borate (100 mL). After maintaining -78 °C and stirring for 1 h, the solution was transferred to a solution of THF (100 mL) containing trimethyl borate (15 mmol). The reaction mixture was gradually warmed to room temperature and stirred continuously for 4 hours. Subsequently, the reaction mixture was poured into 3N hydrochloric acid (125 mL) and extracted three times with ethyl acetate. The organic phases were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure to give the yellowish white solid product 2-methoxy-5-methylphenylboronic acid (2.2 g, 89% yield). The product was characterized by 1H NMR (300 MHz, d6-DMSO): δ 7.6 (s, 1H), 7.38 (d, J = 2.3 Hz, 1H), 7.19 (dd, J = 8.4 Hz, 2.3 Hz, 1H), 6.87 (d, J = 8.4 Hz, 1H), 3.78 (s, 3H), 2.2 (s, 3H).
